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Test Code ArylA MLD Arylsulfatase A for Metachromatic Leukodystrophy (MLD)

Clinical System Name

Arylsulfatase A (Metachromatic leukodystrophy)




Metachromatic Leukodystrophy

Arylsulfatase A, WBC


Spectrophotometric enzyme assay using p-nitrocatechol sulfate as substrate with inhibition of Arylsulfatase B by NaCl and cold temperature incubation. Detection is at 516 nm.

Sample Requirements

Specimen: Whole Blood

Container(s): Yellow/ACD A or B, Dark Green/Sodium Heparin Tube

Preferred Vol:10.0 mL

Minimum Vol: 6.0 mL


Do NOT use gel separator tubes.


Note: Also acceptable: cultured cells from skin fibroblasts (2 confluent T-25 flasks).


Processing Instructions

Reject due to:

Spin: N



Storage location: Biochemical Genetics Box- RT

Weekend Processing: Contact Chem West (x72565) on dayshift.  If Chemistry team is unavailable, sample should be stored in RT Biochemical Genetics box.


Off-site collection: Do not spin!  Keep at room temperature.  Transport M - Th at room temperature via overnight shipping.


Specimen Type Temperature Time
whole blood Room temp

≤24 hr

  Refrigerated <24 hr

Samples received > 24 hr after blood collection will still be processsed and test performed if possible.


STAT Performed TAT
N Weekly 7-10 days


Contact the Biochemical Genetics Lab for requests outside of stated availability (206) 987-2216.

Performing Laboratory

Seattle Children's Laboratory    


Department:  Biochemical Genetics

Phone Number: 206-987-2216


Reference Range


Specimen Type Normal Range (nmol/17 hr/mg protein)






Method: Spectrophotometry

Analytical Volume:


CPT Codes



Biochemical Genetics Requisiton


On the requisition include clinical information needed for appropriate interpretation. (Age, gender, drug therapy and family history)

Clinical Utility

Metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is an autosomal recessive inherited disorder in which the desulfation of 3-0-sulfogalactosyl-containing glycolipids by arylsulfatase A (ASA) is defective. The clinical onset and severity of MLD is variable. The late infantile form typically presents in the second year of life, the juvenile form presents between age 4 and puberty, and the adult form may present at any age after puberty. Gait disturbance and mental regression are the earliest signs. Depending on the variant, other symptoms include blindness, seizures, and behavioral disturbances. Diagnosis of MLD is complicated by the fact that significant reduction of ASA activity may not prove MLD and that its presence does not exclude it. Significant reduction of ASA activity is observed in individuals homozygous for the pseudodeficiency allele. Normal ASA activity is observed in MLD patients with a deficiency of saposin B. Residual activity  can be detected in patients with late infantile MLD. Arylsulfatase B should always be measured if ASA is deficient.


Multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD) is a rare autosomal recessive disorder characterized by the deficiencies of all 12 known sulfatases and leading to a clinical presentation that generally resembles late infantile MLD. Biochemical confirmation is made by reduced activity of both arylsulfatase A and B.